Multi-layer polypropylene (MLPP) insulation coating is used for thermal insulation of subsea pipelines. However in recent years - with higher wellhead operating temperatures - high temperature (HT) Fusion Bonded Epoxies have been used. This paper describes the author's experience with the MLPP systems over the last 20 years.
Subsea flowlines and risers experience fatigue cycles due to thermal and/or pressure transients or vortex induced vibration (VIV). Tests were performed under constant stress intensity factor (K) levels, in a mildly sour environment and in seawater under cathodic protection to understand the difference in the CRG.
Operators desire extended life of offshore facilities, structures and components to improve affordability, and to increase their availability in later years of operation. Whilst maintenance and replacement of topside facilities is possible, critical to this objective is the design and construction of supporting infrastructure and facilities capable of withstanding splash and tidal zone corrosion for the lifetime of the structure with minimum maintenance.
Thermally sprayed aluminum (TSA) is increasingly applied in marine environments as a corrosion mitigation solution but few studies provide quantitative corrosion rate data, from which a lifetime of little or no maintenance can be predicted. A technology review was undertaken to establish current working practice and experience related to the mitigation of splash and tidal zone corrosion. A number of coating systems (thermally sprayed, organic paints and duplex combined thermal spray and paint), currently used in the splash and tidal zone of offshore structures, were identified. Thermal spray coatings with and without aluminum-silicone sealant were prepared and tested in alternate immersion using linear polarisation resistance (LPR) methods. The data were analysed and corrosion rates values were obtained.